Why are parts of the human body not suitable as units of measurement? How did people overcome this problem?

How to lay out the answer. Follow the frame, then write it in your own words.

1 · Name body units. Early people used the digit, hand span, foot, cubit and fathom.
2 · Give the problem. These differ in size from person to person, so two people get different results for the same object.
3 · Show it. In the hand span activity, four people measuring one table get different numbers of spans.
4 · Effect on trade. Results could not be repeated or trusted, which caused disputes between buyers and sellers.
5 · The fix. Rulers fixed one standard, such as the Egyptian standard cubit, and copied it onto measuring sticks.
6 · Close. So a unit must be fixed and the same for everyone; today this is the SI system.

Scoring tip: Two reasons plus one example earn the marks; quote the result of the hand span activity if you did it.